A previous Beneficial Microbial Workshop (BMW) was held in Seattle in October 21-24, 2001. A summary of that meeting was recently published in the ASM News (1). The workshop was attended by over 125 investigators and highlighted the research showing that many bacteria can be and are of great benefit to the host. When considered as an integral part of the host, bacterial cells far exceed the number of eukaryotic cells in the body. Biofilms of the mouth and intestines can be viewed as a type of tissue, fully integrated with other anatomical locations and in constant communication with other bacteria and host cells. The evolutionary biologists report that bacteria-host interactions have been a constant source of genetic pressure, and thus not only have bacteria evolved to live with us, we (the hosts) have evolved as well to better live with bacteria. In this regard, the host immune system has "learned" to tolerate and even exploit the commensals and symbiotic microbes. For example, the development of tolerance to beneficial microbes by the innate immune system is now recognized as integral to health, but is not well understood. We propose to hold a second meeting on this topic in 2005 to provide a forum in which scientists from diverse disciplines can discuss the beneficial hostmicrobe interface and develop novel approaches to study this important facet of human health. A meeting centered on beneficial host-microbe interactions is particularly timely because : . It is a scientifically important and exciting area of microbiology that now merits a dedicated and defined research consortium; Despite its importance to human health it remains an understudied area of research in need of additional funding; . A conference is the ideal mechanism to bring together the diversity of disciplines required to fully understand the beneficial host-microbe interface; . It is an intellectually stimulating subject that attracts pioneering graduate students and post-doctoral fellows who will benefit from participation in a focused and dynamic conference;